How to round sharp edges of iregular mesh
You need first to simplify the mesh using Decimate modifier, here are the steps:

1- Use Decimate Modifier, set Ratio to a low value I used 0.042 for this example.


2- Apply the Decimate modifier, then go to Edit Mode, select the edges you want to Bevel.

3- Ctrl + B to bevel the edges, don't use Clamp, but keep an eye on those adjacent edges, a little overlapping will be correct next step.
4- Ctrl + V and select Remove Doubles, fiddle with the amount until you weld very close together vertices, in this example, I used 0.5.

5- Now add a Subdivision Surface Modifier, if you haven't set the shading to smooth yet, it's time to do. This is the final result, of course you can choose the parameters you need for the previous steps, I put the values according to what I think you're looking for.
Hope this helped, Happy Blending!